Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, turbo-machines such as gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine includes an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section progressively increases the pressure of the working fluid and supplies a compressed working fluid to the combustion section. A fuel is mixed with the compressed working fluid within the combustion section and the mixture is burned in a combustion chamber defined within the combustion section to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity.
The combustion section may include one or more combustors annularly arranged between the compressor section and the turbine section. In a particular combustor design, the combustors include one or more axially extending bundled tube fuel injectors disposed downstream from an end cover. The end cover generally includes one or more fuel circuits that provide fuel to a fluid conduit that provides for fluid communication between the fuel circuits and a fuel plenum defined within each bundled tube fuel injector. Each bundled tube fuel injector generally includes a plurality of parallel tubes arranged radially and circumferentially across the bundled tube fuel injector. The parallel tubes extend generally axially through the fuel plenum to provide for fluid communication through the fuel plenum and into the combustion chamber. The compressed working fluid is routed through inlets of each of the parallel tubes. Fuel is supplied to the fuel plenum through the fluid conduit and the fuel is injected into the tubes through one or more fuel ports defined within each of the tubes. The fuel and compressed working fluid mix inside the tubes before flowing out of a downstream end of the tubes and into the combustion chamber for combustion.
In particular configurations, a cap assembly extends radially and circumferentially across the bundled tube fuel injector generally proximate to the downstream ends of the tubes. The cap assembly generally includes an aft plate having a plurality of tube passages. Each one of the tubes extends at least partially through a corresponding tube passage. The aft plate generally serves as a heat shield between the hot combustion gases and/or a combustion flame and the bundled tube fuel injectors. In order to cool the downstream ends or tips of the tubes, cooling air is routed through a gap provided between the tube and the aft plate. Due to various factors such as thermal growth of the tubes and or the cap plate and/or manufacturing tolerances, the gap around the perimeter of the tubes may vary significantly. As a result, the cooling air may be biased to one side or portion of the tube tip, thus providing uneven cooling to the tube tips. Uneven cooling of the tube tips may result in accelerated wear of the tube tips and/or oxidation of the tube tips. Therefore, an improved cap assembly that provides for even cooling of the downstream end or tip of the tubes of a bundled tube fuel injector would be useful.